Employ the N-Nitrosobis (2-oxopropyl) amine (BOP) hamster model for pancreatic carcinogenesis in retinoid inhibition studies of the carcinogenic process. In these efforts, employ two dose levels of carcinogens (BOP) which results in different tumor incidences. Conduct anticarcinogenesis studies on at least four retinoids. Observe animals in initial studies for life and determine incidence, localization, size, and type of lesion for each experimental group histopathologically. Conduct serial sacrifice studies as may be indicated to define mode of retinoid action as to arrest, regression, delay, or other modification. Employ standard laboratory hamster chow diet in initial series of experiments. Use analytical procedures as proposed for serum glutonic pyruvate transferase and for determination of retinoids in diets. Analyze chemical and histopathology data according to accepted biostatistical procedures.